The present invention relates to the field of optical wireless communications, and in particular to acquisition, tracking, and pointing (ATP) systems for free space optical (FSO) communications.
FSO systems employ light propagating in free space to transmit data without using a connecting cable or transmission line. An FSO system typically consists of a set of two transmitting terminals and receiving terminals or transceiver terminals. Electrical communication signals are converted to optical signals, and then transmitted from the telescope of the transmitting optical terminal. The receiving terminal receives the incoming optical signal into a receiving telescope, which focuses the signal into an optical focal plane for coupling into a photodetector, which then converts the light energy back into an electrical signal.
In order for a receiving terminal to receive an optical signal from a transmitting terminal, the terminal telescopes must be properly aligned. ATP components provide the beam steering necessary for optical telescopes in FSO systems. ATP components act to steer a transmitting telescope or receiving telescope, or both, to point in a desired direction.
Beam steering in optical systems may be accomplished by changing the refractive index of the medium through which the beam is transmitted, or by the use of mirrors or lenses. One existing beam-steering solution is motorized gimbals. A gimbal is a mechanical apparatus to allow a suspended object to rotate freely along two simultaneous axes, within a defined angle of view. A gimballing system used for the alignment of an optical transmitter or receiver typically moves the entire transmitting or receiving telescope through the required field of view. Often, the transmitter and receiver telescopes are mechanically coupled so that the transmitted beam is in the exact direction of an incoming optical beam for collection by the receiving telescope, and thus the two telescopes operate with a common gimballing system.
Gimbal-based FSO systems may be quite heavy due to the weight of the mechanical components, motors, and servos. Gimbal-based systems may also be bulky due to the required mechanical components. Finally, mechanical gimballing systems may require the use of a great deal of electrical power, far more power than is typically consumed by the electronics associated with an optical receiver or transmitter system.
As an alternative to gimbal-based FSO systems, U.S. Pat. Nos. 7,224,508, 7,612,317, 7,612,329, and 8,160,452 teach beam steering by moving an optical fiber in the x-y focal plane of the receiver telescope, including, for example, the use of micro-electro-mechanical systems (MEMS) components to position the optical fiber.